[fitsbits] The CONTINUE and HIERARCH Conventions Public Comment Periods

[William Pence]

Rob Seaman wrote:
>> If we really want to extend FITS to allow longer
>> keyword names, then I think a much simpler way to do this is to just
>> allow free-format keyword records in which the "=" can appear anywhere
>> after byte 9 of the record, such as:
>>
>> MY_LONG_KEYWORD = 17 / comment string
> 
> Bleh!  No, no, no.  Talk about needing to version FITS...

Why would versioning be necessary if this were to be adopted (not that 
this is being seriously proposed)?  I would think that adding a version 
keyword to the new FITS files would only be necessary if there were 
existing FITS files that would be invalidated, or potentially 
misinterpreted, if read using the new free-format keyword parsing rules.

>> Note that this keyword is perfectly legal under the current FITS
>> Standard: existing FITS readers should interpret this as a
>> commentary-type keyword, with the 8-character name "MY_LONG_"
>> and the rest of the record treated as a comment string.
> 
> I don't think we've ever tested this in anger.  A lot of FITS  
> applications likely still assume that the only commentary keywords  
> are COMMENT, HISTORY and <BLANK>.  

Hopefully the FITS Standard is clear that if a keyword does not have a 
"= " value indicator in bytes 9 and 10 of the record, then the keyword 
does not have a formal value.  The new wording in section 4.1.2.3 of the 
proposed new FITS Standard is:

"In keyword records without a value indicator, bytes 9 through 80 should 
be interpreted as commentary text, however, this does not preclude 
conventions that interpret the contents of these bytes in other ways".

The HIERARCH and CONTINUE keyword conventions are examples of this.

As an important reminder, this proposed change in the wording of the 
FITS Standard, along with hundreds of other changes, are all available 
for review and public comment at 
http://fits.gsfc.nasa.gov/fits_draft.html until the end of this month 
(September).

I would like to strongly encourage members of the FITS community to 
carefully read the entire new proposed Standard, and not just the short 
summary documents that the technical panel prepared, to double check 
that all of the proposed changes are clear and that they do not 
inadvertently introduce undesirable changes or ambiguities.

Bill Pence
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)